As of now, only a clickable link can be inserted into an eBlast.  I receive many emails/eBlasts with a bight color 'Donate' button right in the text.  This looks much more polished than a long link.  I am actually quite suprised that eTapestry doesn't already have this capability.   Savvy online donors want quick and easy!  A 'Donate' button is just that...quick and easy!